Our research aims to develop and evaluate methods for selectively and covalently labeling proteins with designed synthetic molecules. Selective labeling of proteins with synthetic molecules is of considerable interest because protein-synthetic molecule conjugates can be used in the study of fundamental biological questions, disease mechanisms, and therapeutic strategies. In our strategy for the development of the labeling systems, proteins and peptides that selectively and covalently react with designed synthetic compounds will be generated using reaction-based selections from combinatorial libraries of antibodies, ankyrin repeat proteins, and other proteins and peptides. The selected protein or peptide will be fused to a protein of interest by protein engineering and the fusion protein will be covalently modified with molecules containing the designed moiety used for the selection. While conventional residue-specific modification methods, such as modification of lysine or tyrosine residues, label most of those surface residues of many proteins, our methods will selectively label the fusion between the protein of interest and the developed protein or peptide tag. The fusion protein will be covalently labeled with the designed compound without requirement of additional reagents or catalysts. The designed compound used for the selection can be conjugated to a variety of molecules including biotin, fluorescent molecules, and cytotoxic molecules. We will validate our labeling systems and demonstrate the use of our labeling systems in labeling of cancer-targeting antibody molecules. Our labeling system will also be used for visualization of a protein of interest in cells using fluorescent molecule-designed compound conjugates. We will also develop peptides that form a covalent bond with designed synthetic molecules only when bound to a protein of interest but not in the absence of that protein; in this system, pre-formation of a fusion protein between the protein of interest and the protein or peptide tag will not be required. [unreadable] [unreadable] [unreadable]